Technical Studies

The purpose of this study is to examine the regulation planning rules of hyperconcentrated flow, through the understanding on the transport behavior by means of characteristic analysis of hyperconcentrated flow, the numerical simulation and the physical model test. The outcome from the theoretical analysis and scenarios application is expected to provide the engineers as a guideline for their design and planning needs. The study will be accomplished in three years. The work scope of first year includes collection of data about hyperconcentrated flow, qualitative analysis of the hyperconcentrated flow, the establishment and testing of numerical model, the planning of physical model and the preliminary proposition of regulation planning rules for hyperconcentrated flow.

The difficulties in understanding hyperconcentrated flows may include: incompleteness in theory, lack of measured data, unavailability of numerical models, and indecisive rules of regulation planning. This project employs the characteristic analysis, numerical modeling, and physical model testing to examine the existing rules of regulation planning to hyperconcentrated flows. Considering the demand of the authorized agency, the goal of this study was restricted to understand the rheological relation of hyperconcentrated fluid and its application to the mild slope in downstream watershed. Basic features of 353 mountain creeks including 19 debris hazards events were collected. Area of landslide, degree of slope, and area of watershed were chosen to be the criteria indices.

To build the framework of potential hyperconcentrated flow criterion, this project applies “Monte Carlo simulation-based parametric optimization” method with criteria indices of the 19 debris hazards events to determine the upper-bound and lower-bound. The rainfall is also chosen as the criterion of the occurrence of hyperconcentrated flow. The result of analysis shows the higher degree of potential-river requires the more intense rainfall.

The physical experiment includes incipient threshold and rheological tests. The current outcome obtained is the physical properties testing including specific weight and size distribution for the sediment sample collected from Dongpuruei River.

The numerical models exploited in this project are the 2-D hyperconcentrated flow model and the 3-D multi-phases flow model (CFX-4).The 2-D model developed is based on the framework of RESED2D model(Hesieh,2002) with the hyperconcentrated flow rehological relation and the supercritical flow treatment embedded. With aspect to the various rehological relation, including arise of water, the superelevated depth and the delay of flow have been observed and examined. The result shows the denser hyperconcentrated flow may cause higher water rise, reducing superelevated depth and slowing down the rate of flow. Under the various conditions of supercritical flow, the simulation results have been verified and agreed well with the experimental data. The above mentioned 3-D model is used to investigate the transport characteristics, so far preliminary analysis on deposition, erosion, and consolidation of hyperconcentrated flow has been carried out.

The incident of dike broken in Mujiliau creek was simulated by utilizing Cell model (Yang, 1992). The result of the above simulation indicates that the flow rate of hyperconcentrated flow may be considered as 1.4 times of the rate of clean water. The correlation between impact force and stability of protection works is also established. By the deduction of the above correlation of the collection of parameters needed, the regulation planning rules maybe well established with sufficient references provided by this project.